1. Field of Invention
The present invention relates to a light-to-voltage converter, and more particularly to an optical input preamplifier of an optical receiver, which comprises a feedback circuit incorporating with a current-to-voltage converter for substantially reducing the impedance input thereof so as to enhance the sensitivity of the optical input preamplifier.
2. Description of Related Arts
Optical receivers are commonly used as a data transmission apparatus. A conventional optical receiver generally comprises a photodiode which receives an optical signal and outputs a photocurrent, and an optical input preamplifier for converting and amplifying an optical signal into an electrical signal. Accordingly, the optical input preamplifier is one of the major factors to determine the sensitivity of the optical receiver.
Since the photocurrent is directly be converted and amplified into the electrical signal, the optical input preamplifier must provide a low noise, high cut-off frequency and high transcondutance ability so as to provide an accurate output of the optical input preamplifier. Therefore, the cost of the optical input preamplifier is relatively expensive and the structural design of the optical input preamplifier is complicated to be manufactured.
Accordingly, a transimpedance amplifier is commonly used as the optical input preamplifier and a front end of thereof is employed with a metal semiconductor field effect transistor (MESFET) for efficiently converting the optical signal into the electrical signal, wherein the transimpedance amplifier is an amplifier that takes currents as the input and has an output voltage proportional to the input current. However, the common problem of the optical input preamplifier is that the sensitivity of the optical input preamplifier is low in such a manner that the optical input preamplifier may not sufficiently convert and amplify the output signal.